Low FPS from PROwin box

[jal3]

Hey,

 

I have a PROwin M4 box, that i just can't get working properly.

My problem is that i get a 20-30m/s drop (eg. m120 spring shoots 100 m/s, not 120-130m/s). I've changed so many parts related to it now, and i'm at a loss for what's causing it.

 

If you know what's causing it, please help me.

[Lone_Bullet]

Just brainstorming but have you checked the airtightness of the cylinder - cylinderhead?

When you place both parts in th GB shell, both the parts might shift a little, decreasing the airseal.

You could inprove the airseal by applying teflontape around the O-ring of the cylinderhead.

Also, perhaps you've forgotten to grease the all O-rings ? Also the one in the airnozzle.

 

If this doesn't help is it possible that the hop unit is not compatible with the gearbox shell?

The gearbox might be pushing the hop unit forwards, not allowing the airnozzle to make a airtight seal with the hoprubber.

Is the hop rubber in a good state?

 

Hope this helped.

[jal3]

Yeah it's airtight. I've used a very large o-ring, and this thing is so solid you'd think it's one-piece.

I've changed between multiple brands of rubber without change, so i don't think that's the cause.

 

Hmmm, i really hope my hopup is compatible, or otherwise i'm fruitcased. Could you link me to a replacement hopup that will fit?

 

Everything is airtight in testing, but when i shoot, it's not.

[Maekl]

Check if your piston can move freely in its rails. The rails on the prowin gearbox are a little too tight for most pistons if I remember right..

[jal3]

Yeah it is. Piston moves freely though, because i've grinded it to fit. I've also tested with a TM piston, which works perfectly without mods (FPS still the same though).

[gzus11]

is it consistent fps every shot and every time you reassemble the box?

get a stronger spring.

[jal3]

How will a stronger spring make it more airtight? Testing from m100 to m170, the velocity drop is consistent.

[Crimson]

Pro wins are a *badgeress* to set up and get working correctly

 

where do you live buddy ?

 

I have owned 4 of these and only managed to get 1 to work, the other 3 i sent to my gunsmith he works wonders on them and charges a fair bit though

[jal3]

Denmark hehe...

I agree. There's a lot of small details, but i've worked them out and this seems to be the only problem left. I've shot a lot of rounds through it. It's precise, stable and just spins, but i've never been able to avoid the 25m/s drop in velocity.

 

The (relevant) parts are:

KM 363mm barrel

Area 1000 hopup packing

Area 1000 roll

Madbull barrel clip (barrel is locked with a screw anyway)

PSEM nozzle, tight o-ring

PDI cylinderhead (original

PDI cylinder (M4 barrel)

JG piston head (don't ask)

Custom 0-ring, flat front

PSEM Piston

 

I'm relatively capable of working with gearboxes, but i just can't figure out this one problem. Thought it might be PROwin specific, since i'm experiencing the same problem on the grey box.

[jal3]

I think i bought the grey one from you, Crimson. Was it assembled by that mechanic you're talking about?

[Lone_Bullet]

Like I said, I was just brainstorming . I don't have a clue what hopup unit would work... .

Could you ask other prowin GB owners?

[gzus11]

if the gb is consistent after all the work, air sealing etc etc your spring

is not giving you what you want, thus get a different spring to give the m/s

you want

 

m120 is a rating, given by the manufacturer, tested in a specific way, all the

variance out there will behave differently in each set up. or possiby you have

a faulty spring unable to produce optimum power

[Maekl]

Check if the nozzle is long enough to create good enough seal with the bucking.

[ertgunner]

i had the same problem, it turned out to be the bucking. After fitting a old guarder it worked flawlessly (unknown spring m120?)370 w/ a .25

[Crimson]

No it was not i assembled my the mechanic as it was working fine in mine

 

change the bucking to TM bucking then cut of 3mm from the end that should solve the air loss

[jal3]

Both are tight now, and the grey one is putting out 185m/s with an M170 spring. It seems dimensions around the hopup unit are way off, and the standard parts have zero chance of working.

 

And you weren't joking when you said "ready to fire, just put it in and it will fire" about the grey one; your mechanic had short-circuit soldered the triggerset

[sadigh]

On mine, I found the cause of the problem was the tappet plate return spring. The supplied pro-win one wouldn't return the tappet plate and nozzle fully forward, maybe by 0.5mm or so, which caused loss of FPS.

 

I cut two coils from it and now its much better, especially on full auto. Also, the red madbull 'velocity enhanced' hop rubbers work wonders in this gearbox!

[DFM56]

If the air nozzle is not transparent, you can shine a light in the magwell when the nozzle is fully forward and look directly into the bore while in a dark room. If the nozzle is not far enough into the bucking, you will be able to see a ring of light in the hop-up chamber. If you've gone over the gearbox as well as you've said, I'm betting the issue is the seal between the bucking and nozzle.